1. Field of the Invention
The present invention relates to a variable-magnification optical system for use in a lens unit or the like, and also relates to an image-taking apparatus incorporating such a variable-magnification optical system.
2. Description of Related Art
In recent years, as personal computers (PC) become widespread, digital still cameras (image-taking apparatuses), which permit easy capturing of images, have been becoming increasingly popular. In such digital still cameras (DSCs), as in cameras using silver-halide film (silver-halide cameras), compactness (slimness) and high performance (for example, a high magnification variation ratio and high aberration correction performance) are sought. Accordingly, compactness and high performance are sought in lens optical systems (for example, variable-magnification optical systems) incorporated in digital still cameras.
To meet such requirements, there have been developed lens optical systems whose total length is shortened by the use of an optical prism or a reflective mirror that bends the light beam traveling from object side to image side (as proposed in, for example, Patent Publications 1 and 2 listed below). The thus shortened total length permits such a lens optical system to be properly arranged within the limited space inside the housing of a DSC. This helps make the housing, and thus the DSC as a whole, compact and slim.                Patent Publication 1: Japanese Patent Application Laid-open No. 2002-169088 (laid-open on Jun. 14, 2002)        Patent Publication 2: Japanese Patent Application Laid-open No. 2000-187159 (laid-open on Jul. 4, 2000)        
Certainly, the lens optical systems proposed in Patent Publications 1 and 2 are compact. These, however, are designed to offer zoom ratios of 7× to 10×, and therefore do not offer satisfactorily high performance.